This invention relates generally to polyester resin systems, and more specifically relates to a process wherein unsaturated polyester resin systems are modified to provide curable, stable water-in-oil emulsion systems, which modified systems may include high percentages of added water.
Unsaturated polyester resins have found application in myriad environments, including e.g. in the fabrication of furniture and of similar structures, wherein the thermoset resin provides characteristics which may be highly simulative of wood, or of other materials commonly utilized in these objects. Similarly, such resins are widely utilized in the manufacture, as e.g. by casting, of a large variety of other products including bowling balls, simulated marble, pistol grips, pearlescent buttons, etc.
In a typical, commercially available unsaturated polyester resin system, a linear polyester resin is combined with a cross-linking monomer, the system sometimes including as well, inhibitors which retard cross-linking until the resin system is ready for use by a fabricator. The linear polyester resin is typically produced by reacting at least one dihydric alcohol with at least one dibasic or dicarboxylic acid. Either the alcohol and/or the acid is ethylenically unsaturated. The resultant unsaturated resin will cure or cross-link with adjacent polyester chains of similar structure by direct reaction, or more commonly through the double bond provided by the ethylenically unsaturated monomer, such as styrene. Other typical monomers include vinyl toluene, methyl methacrylate. .alpha.-methyl styrene, divinyl benzene, dichlorostyrene and diallyl phthalate. Conventional inhibitors include hydroquinone, quinone, and t-butyl catechol.
It is also known to incorporate in the polyester resin system, various extenders and fillers. Among these are e.g. calcium carbonate, clays, talcs, hydrated alumina, antimony oxide, and various organic fillers - such as e.g. pecan shell flour. These fillers may serve to reduce cost or to modify physical characteristics of the resin, or may serve to reduce shrinkage during curing, or to provide or enhance flame retardance.
Additional background information regarding polyester resin systems, their preparation, use polymerization, etc. may be found in such well-known reference works as Polyester Resins by John R. Lawrence, Reinhold Publishing Co. (1960).
Particularly within recent years, the precipitously escalating costs of petrochemicals has generated increasing interest in formulations which might serve to reduce the cost of the polyester resins. Among the concepts that have stimulated great interest, have been reported techniques wherein polyester resins are modified by incorporation of substantial quantities of water to thereby form so-called water-extended polyester resins, known in the art by the designation "WEP." Techniques for preparation of these types of formulations are set forth in many publications, including e.g. in U.S. Pat. Nos. 3,256,219 and 3,666,697. Similarly, reference may be had to such articles as R. H. Leitheister et al "Water-Extended-Polyester Resin," 25 SPE Journal 41 (1960).
In many of these prior art techniques water can only be added to the polyester resin by means of high agitation which is a cumbersome and costly technique. In many instances, further, the stress characteristics of the cured products yield by these water-extended resins have been relatively low. Moreover, the stability of the water-in-oil emulsions particularly where produced by the agitation process have been relatively low. Thus, in these cases the emulsion is broken quite readily upon the addition of conventional fillers particularly if such fillers are organic. While methods have recently been reported which enable production of oil-in-water emulsions with limited agitation, numerous of such technique yield modified resin systems having undesirably high viscosity.
Finally it may be noted, that one of the principal difficulties encountered where use of synthetic resin compositions are contemplated, has been the undersirably high flammability of many of these resins, including particularly many of the polyester resins to which the present invention appertains. Among the techniques heretofore utilized for reducing flammability of such unsaturated polyester resins, has been the attachment of chlorine onto the polyester molecule. Other elements that have been similarly used for such purposes, include bromine, phosphorous, and antimony. Thus in a typical procedure where chlorine is used, sufficient of the gas may be added to a polyester dissolved in a solvent, to form a polyester containing 10 to 60% halogen, with the mixture being maintained at suitable temperatures until the desired degree of halogen addition is obtained, after which the solvent is removed to yield the halogenated polyester. The use, however, of the aforementioned fire retardant agents, notably chlorine and other halogens, creates very undesirably handling problems arising from the highly caustic and toxic nature of these elements; and particularly in recent years, the environment impact of such techniques have become of increasing concern.